Although not accepted universally, the current theory regarding sids
is the rebreathing of co2
which is normally exhaled with each breath by all humans.
The idea is that sids is caused by the rebreathing of co2, in the prone position. Co2, which is a respiratory depressant, is rebreathed when infants inhale from a pocket of exhaled co2. This is why fans, and supine positioning is recommended.